The specification relates to a printing cylinder with a cylinder core of metal, on which a carbon fiber-containing casing is disposed.
In the case of a printing machine, the printing length is determined by the effective diameter of the printing cylinder carrying the blocks. To avoid the need for a special cylinder with the associated bearing constructions for each printing length that may be desired, it is known that an exchangeable casing, which is referred to as a sleeve and then determines the effective diameter and, with that, the printing length, may be pushed onto the peripheral surface of the cylinder.
In the EP-A-0 732 201, a printing cylinder of this type is described, for which the sleeve has a multilayer construction. Two layers of a composite material, reinforced by carbon fibers, form an interstitial space, which is filled with a plastic foam. The inner surface of the sleeve lies tightly against the peripheral surface of the cylinder core, which consists of steel, so that the relatively high radial forces, which arise during the printing process, can be transferred by the relatively soft foam layer of the sleeve to the rigid cylinder core.
It is a disadvantage of this construction that, with the help of the sleeve, only a limited extension of the printing length is attained, because the thickness of the sleeve would have to be so large for larger printing lengths, that the required deformation resistance and size accuracy of the sleeve could no longer be guaranteed. A further disadvantage consists therein that the exchanging of sleeves is relatively work intensive, since the sleeve lies with all of its surface on the cylinder core and large frictional forces would thus have to be overcome when pushing the sleeve on or pulling it off. To reduce these frictional forces, it is known that compressed air may be passed into the interior of the cylinder core, the compressed air entering over radial openings in the interstitial space between the cylinder core and the sleeve.
In the EP-A-0 769 373, a printing cylinder is disclosed, for which the casing, which determines the printing length, has axle stubs with smaller diameters at both axial ends and is mounted directly in the machine frame. A steel shaft, which extends through the casing and is surrounded by the latter at a distance, serves merely to lift the casing from the bearings during an exchange of casings and to hold it so that it can be pulled axially from the shaft.
It is an object of the invention to provide a printing cylinder, for which, without affecting the printing quality, the printing length can be varied over a wider range by exchanging the casing.
Pursuant to the invention, this objective is accomplished for a printing cylinder of the type described above, owing to the fact that the casing is selfsupporting and held at a distance from the peripheral surface of the cylinder core by disks disposed in the region of the two ends.
In this connection, the expression xe2x80x9cself-supportingxe2x80x9d means that the casing has a sufficiently high inherent stiffness and that, although it is supported only at the ends by the disks on the cylinder core, it can withstand the radial forces, which arise during the printing process, so that the deformations, occurring in the casing, remain within permissible tolerance limits. It has turned out that this property of the casing can be attained through the use of a material, consisting of or reinforced with carbon fibers. Because of the relatively low relative density of such a material, the total weight and the moment of inertia of the casing remain relatively low; this has an advantageous effect on the quiet running of the printing machine and on the handling properties of the casing or of the printing cylinder as a whole. Since the casing is held at a distance from the peripheral surface of the cylinder core, the effective diameter of the casing is not determined only by the layer thickness of the sleeve, as it is in the case of conventional sleeves. Instead, it is determined primarily by the distance between the casing and the cylinder core. This permits the use of casings with relatively large diameters, so that correspondingly long printing lengths can be attained.
A further advantage of the invention consists therein that the casing can be pulled from the cylinder core significantly more easily, since it is supported at the cylinder core only by the disks disposed at the ends, so that only relatively low frictional forces arise.
The two disks may be produced from a material, which differs from that of the casing, such as steel or aluminum. Alternatively, however, they can also consist of the same material as the casing or even be constructed in one piece with the casing. Likewise it is possible to construct disks with bearing journals, with which the casings can be mounted directly in the machine frame.
Preferably, the cylinder core is a printing cylinder, which can also be used without the casing. In this case, the printing cylinder can be adjusted to a minimum printing length, in that the casing is simply omitted. The blocks can then be disposed on a conventional sleeve, which is pushed onto the printing cylinder, Alternatively, however, they can also be clamped directly on the peripheral surface of the cylinder core.
It is furthermore possible to increase the printing length even further by pushing a conventional sleeve on the outer periphery of the casing.
Preferably, in a known manner, the cylinder core has a compressed air line, from which radial openings lead to the peripheral surface. When the cylinder core is used without a casing, it becomes easier to push on or pull off a conventional sleeve. When it is used with a casing, the possibility exists of producing an overpressure in the interstitial space between the cylinder core and the casing. The pushing of a conventional sleeve onto the outer periphery of the casing can also be facilitated by radial openings in the casing. In case of need, the compressed air system can also be used to pretension the casing from inside, in order to affect the bulging.